#include <cstdio>
#include <vector>
#include <stack>

using namespace std;

int n, m;
vector<int> vecini[100005];
int stiva[5000000];

void citire()
{
    int tmp1, tmp2;
    scanf("%d %d", &n, &m);

    for(int i = 0; i < m; i++)
    {
        scanf("%d %d", &tmp1, &tmp2);
        vecini[tmp1].push_back(tmp2);
        vecini[tmp2].push_back(tmp1);
    }
}

void euler()
{
    for(int i = 1; i <= n; i++)
    {
        if(vecini[i].size() % 2 != 0)
        {
            printf("-1");
            return;
        }
    }

    int k = 1;
    stiva[1] = 1;

    while(k > 0)
    {
        int x = stiva[k];

        if(vecini[x].size())
        {
            int dest = vecini[x][0];

            int l = vecini[dest].size();

            for(int i = 0; i < l; i++)
            {
                if(vecini[dest][i] == x)
                {
                    vecini[dest].erase(vecini[dest].begin() + i);
                    break;
                }
            }

            vecini[x].erase(vecini[x].begin());


            stiva[k + 1] = dest;
            k++;
        }
        else
        {
            printf("%d ", x);
            k--;
        }
    }
}

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);

    citire();
    euler();
    //afisare();

    return 0;
}